1. FIELD OF THE INVENTION
The field of the present invention is traction control methods for vehicles, specifically directed to producing a braking force in drive-wheel brake devices when an excessively slipping tendency has occurred in a drive wheel during operation.
2. DESCRIPTION OF THE PRIOR ART
Such traction control methods have been already known, for example, from U.S. Pat. No. 3,893,535.
The prior art methods disclosed therein include two types: one is to independently control the hydraulic braking pressures for left and right drive-wheel brake devices, and the other is to collectively control the hydraulic braking pressure for the left and right drive-wheel brake devices, both types of methods being effected when an excessive slipping tendency has occurred in a drive wheel in driving operation.
When excessive slipping occurs in the drive wheels of a vehicle travelling on a sloping road or on a road surface with the drive wheels in contact with the road surface at portions with different friction coefficients, the hydraulic braking pressure for the drive-wheel brake devices should be independently controlled in order to rapidly recover the driving force. In contrast, when excessive slipping occurs in the drive wheels in the course of the travelling of the vehicle at a relatively high speed, the hydraulic braking pressure for the drive-wheel brake devices should be collectively controlled so as to maintain the stability of the vehicle. However, if the hydraulic braking pressure is controlled in a fixed control mode as in the prior art, no satisfactory result can be achieved with respect to either the driving force or the stability.